MPLS OAM Technology White Paper - ActForNet
MPLS OAM Technology WhitePaperIssue01Date2012-10-30HUAWEI TECHNOLOGIES CO., LTD.
Copyright Huawei Technologies Co., Ltd. 2012. All rights reserved.No part of this document may be reproduced or transmitted in any form or by any means without priorwritten consent of Huawei Technologies Co., Ltd.Trademarks and Permissionsand other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.All other trademarks and trade names mentioned in this document are the property of their respectiveholders.NoticeThe purchased products, services and features are stipulated by the contract made between Huawei andthe customer. All or part of the products, services and features described in this document may not bewithin the purchase scope or the usage scope. Unless otherwise specified in the contract, all statements,information, and recommendations in this document are provided "AS IS" without warranties, guarantees orrepresentations of any kind, either express or implied.The information in this document is subject to change without notice. Every effort has been made in thepreparation of this document to ensure accuracy of the contents, but all statements, information, andrecommendations in this document do not constitute a warranty of any kind, express or implied.Huawei Technologies Co., Ltd.Address:Huawei Industrial BaseBantian, LonggangShenzhen 518129People's Republic of ChinaWebsite:http://enterprise.huawei.comIssue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.i
MPLS OAM Technology White PaperAbout This DocumentAbout This DocumentAbstract:OAM plays a very important role in the public telecom network, especially for theQoS-guaranteed network. OAM can simplify network operations, test network performance,and reduce network operation costs. As the key bearer technology of the scalablenext-generation network, MPLS can provide multiple services with guaranteed QoS.Therefore, the MPLS network urgently requires OAM capabilities. This document describesthe technical principles, implementation, and typical applications of MPLS OAM.Keywords:MPLS, OAM, PS, CV, FFD, FDI, BDIIssue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.ii
MPLS OAM Technology White PaperContentsContentsAbout This Document . ii1 MPLS OAM Overview . 12 Technology Overview . 22.1 MPLS OAM Overview . 22.2 Protection Switching Overview. 32.2.1 1:1 Protection Switching . 42.2.2 1 1 Protection Switching . 53 Key Technology . 63.1 Example . 63.2 Technology . 73.2.1 CV Monitoring . 73.2.2 FFD Monitoring . 83.2.3 Backward Defect Indication (BDI) . 83.2.4 Forward Defect Indication (FDI) . 93.2.5 Auto Negotiation Mechanism (First-Packet Triggering, Auto-Sensing) . 103.2.6 Binding the Backward Path . 113.3 Terms . 124 Typical Applications . 154.1 Terminal Network Faults . 154.2 Hierarchical OAM . 154.3 Testing the Entire LSP . 165 Conclusion . 176 References . 18A Abbreviation . 19Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.iii
MPLS OAM Technology White Paper1 MPLS OAM Overview1MPLS OAM OverviewMPLS OAM technology provides the MPLS network with a defect-detection tool and adefect-rectification mechanism that are independent of any Layer 3 or Layer 2 protocols. Thecheck function of the CR-LSP forwarding plane is implemented through MPLS OAM andprotection switching. The protection switching is performed 50 ms after a defect occurs sothat the impact of the defect is minimized. This document describes the background andworking principles of MPLS OAM. The intended audience needs to know MPLS and MPLSOAM.The server-layer that bears MPLS, such as SONET/SDH, and the client-layer that uses MPLS,such as IP, FR, and ATM, have their respective OAM mechanisms. Failures of the MPLSlayer network cannot be solved thoroughly through the OAM mechanism of other layers. Inaddition, the network technology hierarchy also requires MPLS to have its independent OAMmechanism to decrease the dependency of layers on each other.In fact, MPLS OAM provides a set of check mechanisms for the MPLS user layer. MPLSOAM is independent of other network layer and provides the state information of LSP forusers, abundant LSP diagnosis interfaces for network management and maintenance personnel,and references for network performance detection and user accounting. While providing acheck tool, MPLS OAM has a complete protection switching mechanism and can switch userdata within 50 ms after the MPLS layer detects defects, which minimizes the loss of user data.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.1
MPLS OAM Technology White Paper2 Technology Overview2Technology Overview2.1 MPLS OAM OverviewMPLS OAM checks the connectivity of a single LSP from the source end to the destinationend. As shown in Figure 2-1, the ingress node periodically sends an OAM continuity check(CV) packet and the egress node checks it periodically. The transit node makes pass-throughprocessing. When the destination end detects a defect, it sends Backward Defect Indication(BDI) packets to the LSP source node through the bound return path to fulfill protectionswitching.Figure 2-1 Networking diagram of MPLS OAM connectivity detectionAn OAM packet can be considered as an MPLS data packet, but the OAM packet carriescontrol information. The OAM packet is encapsulated as an MPLS packet on the ingress node.That is, the outer label of the packet is the out-label of the LSP on this node. The inner label isset to 14 (OAM Route alert label). The other bits are the payload of the OAM protocol packet,as shown in Figure 2-2. When the egress node detects a defect, the egress node notifies theingress node using a notification packet. In this way, the source and destination nodes of theLSP learn about the current status of the LSP to provide the client-layer with statusinformation of the entire LSP. The status information helps determine whether to triggerprotection switching.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.2
MPLS OAM Technology White Paper2 Technology OverviewFigure 2-2 Unidirectional check principleFigure 2-3 shows the format of an MPLS OAM packet header.Figure 2-3 Format of an OAM packet headerMPLS OAM packets are differentiated from common user plane traffic by an increase of 1 inthe label stack at a given LSP level at which they are inserted. Compared with a commonMPLS packet, an OAM packet header has the following characteristics: The value 14 in the Label field indicates an OAM packet. The TTL field is set to 1 to ensure that OAM packets are transmitted to the LSR that isthe LSP egress monitored by OAM.An OAM packet is transparent to the transit LSR and the penultimate LSR. MPLS OAMapplies mainly to ER LSPs, which refer to TE tunnels.2.2 Protection Switching OverviewProtection switching is a protection mechanism for complete provisioning and can be used onany topology. The route and bandwidth of the protection LSP are reserved for the workingLSP. When the working LSP is likely to become faulty, protection must be implemented in allcases. Therefore, the protection LSP must be a completely different physical channel in fact.Only in this way can common faults be rectified. In addition, the working LSP cannottransmit packets along the shortest path.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.3
MPLS OAM Technology White Paper2 Technology Overview2.2.1 1:1 Protection SwitchingFigure 2-4 Traffic when links are working properlyCV packet insertionPath Merge LSR with a merging selectorPath Switch LSRWorking LSPWorking trafficWorking trafficProtection LSPCV packet extractionSelectorSource of the protected domainSink of the protected domain Permanent mergeThe 1:1 switching mode indicates that a protection LSP is used to take the place of a workingLSP when the working LSP fails. Working and protection LSPs are established on the ingressnode. When the links are working properly, the traffic is relayed to the working LSP throughthe selector on the ingress. The protection LSP does not have the traffic that is transmitted onthe working LSP.Figure 2-5 Traffic when the working LSP is faultyCV packet insertionPath Merge LSR with a merging selectorPath Switch LSRWorking LSPWorking trafficWorking trafficProtection LSPCV packet extractionSelectorSource the of protected domainSink of the protected domain Permanent mergeAfter the egress node finds that the link on the working LSP has failed, user data is switchedto the protection LSP. The egress node sends BDI packets to the ingress node through thebackward path to request the ingress node to perform the switching.After the ingress node receives the BDI packets, it relays the selector to the protection LSPand switches the traffic from the working LSP to the protection LSP. In this way, 1:1protection is implemented.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.4
MPLS OAM Technology White Paper2 Technology Overview2.2.2 1 1 Protection SwitchingFigure 2-6 Traffic when links are working properlyCV packet insertionPath Switch LSRPath Merge LSRWorking LSPWorking trafficProtection LSPPermanent bridgeSource of the protection domainSink of the protection domain SelectorCV packet extr actionIn the 1 1 architecture, a protection LSP is dedicated to a working LSP. On the source end ofthe protection domain, user data is transmitted to the destination end of the protection domainon both the working and protection LSPs. The destination end selects one from the workingand protection LSPs to receive the user data. In this way, the user services are transmitted onboth the working and protection LSPs. Whether the destination end selects the working LSPor protection LSP to receive data depends on the protection mechanism.Figure 2-7 Traffic when the working LSP is faultyCV packet insertionPath Switch LSRPath Merge LSRWorking LSPWorking trafficProtection LSPPermanent bridgeSource of the protection domainSink of the protection domainCV packet extractionSelectorAfter the MPLS OAM check tool finds that the working LSP has failed, the destination endswitches the path for receiving user data from the working LSP to the protection LSP. In thisway, 1 1 protection switching is implemented. The source end does not perform anyswitching in this case.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.5
MPLS OAM Technology White Paper3 Key Technology3Key Technology3.1 ExampleThe following example illustrates the working principle and process of MPLS OAM.Figure 3-1 Working principle of MPLS OAMP-2CECEPE-APE-BP-1CECEWorking LSPProtection LSPThe red TE LSP (PEA P1 PEB) in Figure 3-1 indicates the working LSP. To protect theworking LSP, an LSP (PEA P2 PEB) with the same source and destination ends needs tobe established, which is indicated in green. 1:1 protection switching is used. The OAM checkfunction is enabled on the working LSP (red). On PEB, the backward LSP of the working LSPis specified. The backward LSP is established in advance and can have the same path as theprotection LSP but in the opposite direction.The working LSP sends connectivity verification (CV) packets at a fixed interval of 1s onPEA. The destination end specifies a slide window of 1s. The destination end monitors andstatistically analyzes CV packet correctness within 3s. This is the criteria for determining theLSP status.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.6
MPLS OAM Technology White Paper3 Key TechnologyA CV packet is a low-rate check packet and cannot meet the requirements for fast switchingin some important scenarios. Therefore, it is recommended to use the fast failure detection(FFD) packets with a higher transmission rate instead of CV packets. The working LSP sendsFFD packets periodically at a fixed rate on PEA. The destination end monitors andstatistically analyzes FFD packet correctness within a period three times the check interval.This is the criteria for determining the LSP status. The FFD packets have the same functionswith CV packets, but have an adjustable rate and a shorter check interval.After the destination end detects a defect on PEB, the destination end sends BDI packets tothe source end through the backward path. The backward path must be an LSP. In thisexample, the backward path is from PEB to P2 and then to PEA. After the source end receivesthe BDI packets, it locates the working LSP according to the packet information and performsthe switching according to the corresponding information about the protective group. That is,the user data is switched to the protection LSP for transmission.3.2 TechnologyThe preceding example illustrates the following key technologies of MPLS OAM.3.2.1 CV MonitoringThe LSP source node sends CV packets a fixed interval of 1s. The destination end monitorsand statistically analyzes CV packet correctness within a period three times the check interval.This is the criteria for determining the LSP status. A CV packet is usually used for theavailability detection of a common LSP because the generation rate is low and cannot beadjusted. Figure 3-2 shows the format of a CV packet. The Function Type field is fixed at0x01.Figure 3-2 Format of a CV packetIssue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.7
MPLS OAM Technology White Paper3 Key Technology3.2.2 FFD MonitoringFFD provides the detection mechanism for the LSP of the P2P type. The LSP source nodeperiodically sends FFD packets at a configurable rate of 10 ms, 20 ms, 50 ms, 100 ms, 200 ms,or 500 ms. The destination end monitors and statistically analyzes FFD packet correctnesswithin a period three times the check interval. This is the criteria for determining the LSPstatus. The FFD packets have the same functions with CV packets, but have an adjustable rateand a shorter check interval. Therefore, FFD packets apply to the check of an LSP in Serverstate. Figure 3-3 shows the format of an FFD packet.Figure 3-3 Format of an FFD packetIn an FFD packet, the Function Type field is set to 0x07. Compared with a CV packet, an FFDpacket has one more field (Frequency) that supports multiple sending intervals.3.2.3 Backward Defect Indication (BDI)After the LSP destination end detects a defect, it sends BDI packets to the source nodebackwards. The backward path must be an LSP. The received BDI packets are used to notifythe source node of the LSP failure.Figure 3-4 shows the format of a BDI packet. The Function Type field is set to 0x03. TheDefect type and Defect location fields exist in a BDI packet.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.8
MPLS OAM Technology White Paper3 Key TechnologyFigure 3-4 Format of a BDI packetThe TTSI field in a BDI packet is optional. The TTSI is necessary when a shared backwardtunnel or out-of-band backward tunnel is used. For a bidirectional LSP, this field can be filledwith 0. If the TTSI is used, the value of the field is the TTSI of the LSP. For details, see TTSIindex mode.If the FDI packet reported by the lower level LSP is received, the Defect type and the Defectlocation fields are generated according to the corresponding fields of the FDI packet.3.2.4 Forward Defect Indication (FDI)A forward defect indication (FDI) packet is generated by the LSR detecting defects. An FDIpacket is a response to the defects detected by a CV or FFD packet. For the lower level LSP: The source end of the LSP uses a FDI packet to inform the destination end of the defect. When the auto protocol is enabled, the source end of the LSP requests the destinationend to stop OAM detection.Figure 3-5 shows the format of an FDI packet. The Function Type field is set to 0x02. TheDefect type and Defect location fields exist in an FDI packet.Issue 01 (2012-10-30)Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.9
MPLS OAM Technology White Paper3 Key TechnologyFigure 3-5 Format of an FFI packetThe node that first detects a defect sends an FDI packet to the downstream node. The TTSIfield in the FDI packet is optional. It is used when the penultimate hop popping (PHP) isapplied. In other cases, the TTSI is not used and is set to 0. For details, see TTSI index modesection 3.2.6 "Binding the Backward Path."The FDI packet is reported to one higher level after another. When a higher level LSP detectsdefects by its own CV or FFD packet, the LSP also receives the FDI packet reported by thelower level LSP. Therefore, it can be concluded that the defect occurs at the lower level.The protocol does not include the MPLS OAM notification mechanism. When the MPLSOAM function on the source end is disabled, the destination end still monitors defects at afixed interval. As a result,
MPLS OAM Overview MPLS OAM technology provides the MPLS network with a defect-detection tool and a defect-rectification mechanism that are independent of any Layer 3 or Layer 2 protocols. The check function of the CR-LSP forwarding plane is implemented through MPLS OAM and protection switching.
the OAM PDU, the OpCode field allows identifying the type of OAM frame. The ITU-T OAMs provide a set of mechanisms that meets the MPLS-TP OAM requirements. The methods and procedure supported are listed in Table. 1: TABLE I. G.8113.1 OAM FUNCTIONS [13] Application OAM Function (IETF draft-bhh-mpls-tp-oam-y1731) Fault Management (FM)
Ethernet OAM Decoder Ring IEEE 802.1ag Connectivity Fault Management (CFM) Also referred as Service OAM IEEE 802.3ah (clause 57) Ethernet Link OAM Also referred as 802.3 OAM, Link OAM or Ethernet in the First Mile (EFM) OAM ITU-T Y.1731 OAM functions and mechanisms for Ethernet-based networks MEF E-LMI Ethernet Local Management Interface
MPLS PW OAM mechanisms are described next, and a brief look at existing layer 2 OAM mechanisms is provided. The article goes on to describe the relationship between end-to-end fault detection and the segment-based OAM mechanisms. MPLS PW An MPLS PW is the mechanism used to carry layer 2 traffic over MPLS. It is a point-to-point
slide series thatdescribe the Multiprotocol Label Switching (MPLS) concept . Layer-3 VPNs Layer-2 VPNs MPLS QoS MPLS TE MPLS OAM/MIBs End-to-end Services MPLS Network Services . §MPLS label forwarding and signaling mechanisms Network Infrastructure MPLS Signaling and Forwarding Layer-3 VPNs Layer-2 VPNs
Carrier Ethernet OAM Protocol Positioning E-LMI - User to Network Interface (UNI) Link OAM - Any point-point 802.3 link CFM, Y.1731 PM - End-to-End UNI to UNI MPLS OAM - within MPLS cloud Core Customer MPLS/IP Business Residential Business Residential UNI NNI NNI NNI UNI Customer MPLS OAM .
ATMOAM,SONETOAM,Ethernet OAM,VLANs,L2VPN (TransparentLANServices), etc. The ITU (SG13/Q3.13) recommendations and different IETFRFCsarereferringto OAMfunctions foropticalEthernet, OAM and network management in IP-based and other networks, OAM mechanisms for MPLS networks, and protection switching for MPLS networks. However, since
OAM. MPLS OAM offers similar mechanisms to IEEE 802.1ag: Virtual Circuit Connectivity Verification (VCCV), Bi-directional Forwarding Detection (BFD), LSP ping, and trace-route, which allow the service provider to isolate the fault within the MPLS core. Thus, OAM at each layer in the network helps isolate problems to that layer,
Alfredo López Austin). Co-Edited Volume: Art and Media History –––Modern Art in Africa, Asia and Latin America: An Introduction to Global Modernisms. Boston: Wiley-Blackwell, 2012 (Elaine O’Brien, editor; Everlyn Nicodemus, Melissa Chiu, Benjamin Genocchio, Mary K. Coffey, Roberto Tejada, co-editors). Exhibition Catalogs ––– “Equivocal Documents,” in Manuel Álvarez Bravo (c
